1. Technical Field
The present invention relates to a concentration determination apparatus, a probe, a concentration determination method, and a program for non-invasively determining a concentration of a target component in an observed object in any of a plurality of light scattering medium layers in a living body.
Priority is claimed on Japanese Patent Application Nos. 2010-158097, 2010-158098, 2010-158099 and 2010-158100 filed on July 12, 2010, the contents of which are incorporated herein by reference
2. Related Art
In recent years, diabetics in an age of gluttony continue to increase each year in Japan. Therefore, diabetics with nephritis also continue to increase each year. Patients suffering from chronic renal insufficiency also continue to increase by ten thousand each year and currently number over 280 thousand.
Meanwhile, with the advent of an aging society, a demand for preventive medicine and the importance of personal metabolism management are rapidly increasing. In particular, blood sugar value measurement is important. Glucose metabolism in an early stage of diabetes can be evaluated by blood sugar value measurement. The blood sugar value measurement enables early treatment based on early diagnosis of the diabetes.
Traditionally, the blood sugar value measurement is performed by taking a blood sample from a vein of, for example, an arm or a fingertip and measuring enzyme activity for glucose in the blood. This method of measuring a blood sugar value has various problems, such as that taking a blood sample is complicated and painful, and poses a risk of infection. Further, a measurement tip for adhering blood is required. Thereby, there is a need for a non-invasive blood sugar value measurement method that does not require that a blood sample be taken.
As a method of continuously measuring a blood sugar value, equipment for continuously determining glucose corresponding to a blood sugar value in a state in which an injection needle is pushed into a vein has been developed in USA and is currently in clinical trials. However, since the injection needle is pushed into the vein, there are risks of the needle being left or infection during measurement of the blood sugar value.
There is a need for a blood sugar value measurement apparatus capable of frequently measuring a blood sugar value without taking a blood sample and having no risk of infection. Further, there is a need for a miniaturized blood sugar value measurement apparatus capable of being mounted simply and at any time.
A method of irradiating near-infrared light to skin and obtaining a glucose concentration from a light absorption amount is disclosed in Japanese Patent No. 3931638, for example. In this method, an apparatus irradiates near-infrared continuous light to the skin and calculates a glucose concentration from the light absorption amount. Specifically, a calibration curve representing a relationship among a glucose concentration, a wavelength of irradiated near-infrared light, and a light absorption amount is created in advance. Near-infrared continuous light is irradiated to the skin, and light returned from the skin is scanned in any wavelength band using, for example, a monochromator. A light absorption amount for each wavelength in the wavelength band is obtained, and the light absorption amount in each wavelength is compared with the calibration curve. Accordingly, a glucose concentration, i.e., a blood sugar value, in the blood is calculated.
In general, when near-infrared spectroscopy analysis of a solution or a sample having high moisture content is performed, a spectrum of the sample is greatly shifted due to a temperature change, similar to a spectrum of water. Accordingly, when quantitative analysis is performed using near-infrared spectroscopy, effects of the temperature of the solution or the sample cannot be ignored.
An apparatus for stabilizing a temperature of a contact portion between a measuring surface of a probe tip of a near-infrared light transmitting and receiving optical fiber bundle and tissue near a surface of a living body using a heater and a surface temperature detection means when a glucose concentration of the tissue near the surface of the living body is measured using absorption of light in a near-infrared region is disclosed in Japanese Unexamined Patent Application, First Publication No. 2001-299727.
However, in a conventional method of measuring a glucose concentration in blood or tissue near a surface of a living body from an absorption amount of near-infrared light, a temperature change rate of an absorption coefficient of water contained in the blood or the living body, for the near-infrared light, is great. Thus, it is difficult to accurately measure the glucose concentration in the blood or in the living body.
For example, when a temperature of a contact portion between a measuring surface of a probe tip of a near-infrared light transmitting and receiving optical fiber bundle and tissue near a surface of a living body is stabilized by a heater and a surface temperature detection means, the temperature of the contact portion is reliably stabilized. However, when temperature of the living body is changed, temperature of the tissue near the surface of the living body is also changed and an absorption coefficient for the near-infrared light is changed. It is difficult to accurately measure the glucose concentration in the living body.
Further, in a conventional noninvasive blood sugar value measurement method, a near-infrared absorption spectrum of the dermis is measured by determining a distance between an input and an output of light. For this, the measured absorption spectrum includes an absorption spectrum of an epidermis or a subcutaneous tissue layer as well as the absorption spectrum of the dermis. Noise due to the epidermis or the subcutaneous tissue layer is involved in a change of the observed absorption coefficient.
Further, a conventional glucose concentration measurement apparatus has the following problems.
First, in an apparatus in which a contact portion between a measuring surface of a probe tip of a near-infrared light receiving and emitting optical fiber bundle and tissue near a surface of a living body is heated by a heater, energy for heating the measuring surface in contact with the surface of the living body needs to be supplied, a control means for stabilizing the temperature of the contact portion with the tissue near the surface of the living body is necessary, and the apparatus is expensive and difficult to miniaturize.
Second, the control means for stabilizing the temperature of the contact portion with the tissue near the surface of the living body performs measurement when a near-infrared light receiving and emitting unit are brought into contact with the tissue near the surface, or performs the measurement after the receiving and emitting unit is brought into contact with the tissue near the surface, irradiation of the near-infrared light is initiated and then a given time has elapsed. In addition, the given time is determined based on a target temperature, an ambient temperature, and a living body temperature at a time when the near-infrared light receiving and emitting unit is brought into contact with the tissue near the surface of the living body. Hence, it is necessary to obtain a sufficient thermal equilibrium state until the living body temperature is obtained after the receiving and emitting unit is brought into contact with the tissue near the surface, the irradiation of the near-infrared light is initiated and then the given time has elapsed, after the ambient temperature is obtained when the receiving and emitting unit is brought into contact with the tissue near the surface. Normally, 60 seconds to 120 seconds are needed to obtain thermal equilibrium state.
Thus, it is impossible to miniaturize a conventional glucose concentration measurement apparatus and greatly shorten a measurement time while securing determination accuracy for glucose concentration in a living body.